【作者】 陈雯；

【导师】 贾金青；

【作者基本信息】 大连理工大学 ， 结构工程， 2022， 硕士

【摘要】 在建筑行业,泵送混凝土因其质量稳定、机械化程度高而被广泛应用于高层建筑建设中,但其可泵性随之带来早期开裂、对环境不友好等问题。针对这些问题,基于“粗骨料嵌锁”这一核心理念,后掺骨料混凝土是将商品混凝土泵送到浇筑面后,使用专用绿色设备往里掺入一定比例粗骨料并经历二次搅拌均匀、浇筑和振捣,最终形成的新型混凝土。为研究后掺骨料混凝土抗碳化以及碳化后各性能,本文先设计满足工作要求的普通C40基准混凝土,再通过后掺粗骨料施工工艺,得到不同比例(0%、10%、20%、25%和30%)后掺粗骨料混凝土,研究其在不同碳化龄期(3d、7d、14d和28d)时的碳化深度、p H值、抗氯离子渗透能力,抗压、抗劈裂和抗折等力学性能以及完全碳化后的弹性模量,并将试验结果对比分析。根据试验得到的碳化深度数据,采用现存混凝土碳化模型和回归拟合方法,得到后掺骨料混凝土碳化深度的预测模型。结合大连环境修正系数,建立后掺骨料混凝土碳化深度平均值公式并预测500年后各后掺率的平均碳化深度。最后计算后掺骨料混凝土碳化寿命。研究表明:(1)各后掺率的碳化深度值都随着碳化时间的延长不断增加,随着粗骨料后掺比例提高,达同一碳化龄期的碳化深度呈下降的趋势。30%的后掺率抗碳化性能最优。(2)随着碳化时间的增加,后掺骨料混凝土的表观孔隙率与内部孔隙率降低,p H值与OH~-浓度也降低;后掺率为0%的碳化周期结束时p H值降至钢筋开始锈蚀,但混凝土保护层未全消失。(3)随着碳化反应的进行,后掺率为25%的混凝土6h内电通量增大,抗氯离子能力下降。(4)碳化后的抗压和抗劈拉强度随碳化时间的延长而提高,随碳化深度的增加而增大;抗折强度则随时间与随碳化深度的增加都呈先增后降趋势,最终低于未碳化时的抗折强度,不同的后掺率出现下降段时碳化深度不尽相同。(5)完全碳化的后掺骨料混凝土弹性模量提高了约20%～45%,弹性模量的变化趋势正比于抗压强度的变化。(6)建立的后掺骨料混凝土碳化模型发现,碳化深度与碳化时间的0.25～0.35次方成正比,后掺骨料影响因子随粗骨料掺量的增大而下降。(7)后掺骨料混凝土碳化深度平均值公式预测500年后后掺混凝土碳化深度,均未超混凝土保护层。在后掺骨料混凝土碳化寿命两个阶段,后掺率的提升对第二阶段寿命的增加更明显。建立的后掺骨料混凝土碳化深度模型为后掺骨料混凝土结构抗碳化后续研究提供参考。更多还原

【Abstract】 In the construction industry,pumped concrete is widely used in the construction of high-rise buildings because of its stable quality and high degree of mechanization,but its pump ability brings about problems such as early cracking and being unfriendly to the environment.In response to these problems,based on the core concept of "coarse aggregate interlocking",after-mixing coarse aggregate concrete is to pump the commercial concrete to the pouring surface,use special green equipment to mix a certain proportion of coarse aggregate into it,and undergo secondary The new concrete is finally formed by mixing,pouring and vibrating.In order to study the anti-carbonation and properties of after-mixing coarse aggregate concrete,this paper first designs ordinary C40 benchmark concrete that meets the working requirements,and then obtains different proportions(0%,10%,20%,25% and 30%)were mixed with coarse aggregate concrete,and its carbonization depth,p H value,resistance to chloride ion penetration,compression resistance,split resistance and the mechanical properties such as bending resistance and the elastic modulus after complete carbonization are compared and analyzed.According to the carbonation depth data obtained from the test,the existing concrete carbonation model and the regression fitting method are used to obtain the prediction model of the after-mixing coarse aggregate concrete carbonation depth.Combined with the Dalian environmental correction coefficient,the formula of the average carbonation depth of after-mixing coarse aggregate concrete is established and the average carbonation depth of each after-mixing coarse aggregate rate is predicted after 500 years.Finally,the carbonation life of after-mixing coarse aggregate concrete was calculated.The results show that:(1)The carbonization depth value of each after-mixing rate increases with the extension of carbonization time.With the increase of the after-mixing ratio of coarse aggregate,the carbonization depth at the same carbonization age shows a downward trend.(2)With the increase of carbonization time,the apparent porosity and internal porosity of after-mixing coarse aggregate concrete decreased,as well as the p H value and OHconcentration;at the end of the carbonization cycle with a after-mixing coarse aggregate rate of 0%,the p H value dropped to the steel bar and began to corrode,but the concrete protective layer has not completely disappeared.(3)With the progress of carbonization reaction,the electric flux of concrete with an after-mixing rate of 25% increased within 6 hours,and the resistance to chloride ions decreased.(4)The compressive strength and splitting tensile strength after carbonization increase with the prolongation of carbonization time and increase with the increase of carbonization depth;the flexural strength increases first and then decreases with the increase of time and carbonization depth.The ultimate flexural strength is lower than the un-carbonized flexural strength,and the carbonization depth is different when different after-mixing rates appear in the descending stage.(5)The elastic modulus of the fully carbonized after-mixing coarse aggregate concrete increases by about 20% to 45%,and the change trends of the elastic modulus are proportional to the change of the compressive strength.(6)The established after-mixing coarse aggregate concrete carbonation model shows that the carbonation depth is proportional to the 0.25-0.35 power of the carbonization time,and the after-mixing coarse aggregate influence factor decreases with the increase of the coarse aggregate content.(7)The average formula of carbonation depth of after-mixing coarse aggregate concrete predicts the carbonation depth of after-mixing coarse aggregate concrete after 500 years,none of which exceeds the concrete protective layer.In the two stages of carbonization life of after-mixing coarse aggregate concrete,the increase of after-mixing rate has a more obvious increase in the life of the second stage.The established after-mixing coarse aggregate concrete carbonation depth model provides a reference for the follow-up research on after-mixing coarse aggregate concrete structure carbonation resistance.更多还原